Over the past seven days, the issue of morality has boldly taken its place in the business of politics. Last Sunday, for example, President Obama said of the contrast between Democrats and Republicans: "This is a contest of values. This is a choice about who we are and what we stand for." Two days later, Ed Miliband, the Labour leader, criticised rampant "fast-buck" capitalism while trying to define a fairer settlement between rich and poor, citizen and state. "Something for something," he instructed. It might therefore appear an omission on the part of David Cameron if, at the Conservative party conference in Manchester, he fails to make his own contribution to the current redefining of the political debate.

The prime minister is liked by the electorate and therefore stands a greater chance of being heeded. Polling conducted by Lord Ashcroft, former deputy Conservative chairman, reveals that voters describe Cameron as "determined", "competent" and "ruthless", a "tiger" of a man. (Nick Clegg, Cameron's other half in the coalition, fares less well, described as a "puppet".) More than half of the electorate claim Mr Cameron would make the best prime minister, compared with 34% for Mr Miliband and 12% for Mr Clegg. However, complacency is always unwise in politics.

The polling also revealed that only 27% of the electorate believe Conservatives are "on the side of ordinary people", while a recent YouGov survey found that 42% said they would "never" vote Tory. In addition, the Observer today reports on the growing disaffection of women, especially among skilled manual workers (C2s), the vital group to deliver marginal constituencies. Stir into this the growing interest in citizenship and a reformed capitalism and the Observer suggests that Mr Cameron may feel obliged in his speech on Wednesday to expand further on what precisely he means by "modern, compassionate Conservatism". Is it critical of crony capitalism? Is it as interested in the wellbeing of all as it is in unfettering the market?

We have a clue in the idea of the big society. As Mr Cameron has pointed out in one of its several relaunches, it is not "a fluffy add-on" to government but at its very heart. It is liked by the public, local authorities and business leaders. However, while the rhetoric is welcomed, its reality is not. In one poll, only 13% of the population believe the coalition has a clear plan for the implementation of the big society.

In a speech last year, Mr Cameron expanded on what the big society means in practice: a change from "state power to people power". Social action, public service reform and community empowerment will shrink the state. What remains of government will be used for "galvanising, catalysing, prompting… community engagement and social renewal". Helped by the big society's handmaiden, the Localism Bill, power will be devolved from central government to, for instance, local organisations so they can take over and bid to run local assets and services. Councils, in theory, will have more control over how they spend their budgets. Trust, sympathy and altruism will replace rampant greed; "Broken Britain" will be fixed.

Now, big society capital is dispensing loans, community organisers are recruiting volunteers and four "vanguard communities" are engaged in transforming the welfare state. One of Mr Cameron's influences is David Brooks, a rightwing American columnist, who advocates "a party of community and civic order" that replicates "the gatherings at the local barber shop and the church social, the gossip with the cop and the bartender".

The challenge for Mr Cameron is that the big society was born in austerity. Only twice before have we experienced cuts to public services for two years in succession. We now face several years with more than £17bn axed from welfare spending. At the same time, the Observer believes Mr Cameron's renowned lack of attention to detail, and a casual disregard for consequences (perhaps his wealth has immured him from the habit), means that the very values that the big society is intended to inculcate and cherish are being rapidly undermined, widening inequality and accelerating social injustice.

Research by John Mohan of the Third Sector Research Centre says that 31% of the population provide 87% of volunteering hours. They are mostly middle class in middle-class areas. In deprived neighbourhoods, volunteering is less common. It is also these areas that have been hit hardest by the cuts. Simultaneously, the National Council for Voluntary Organisations has reported, for the first time in years, a 5% drop in volunteering. Charities and organisations are concerned about their capacity to meet rising demand. This is illustrated by the pressure on food resources reported by Jay Rayner in the Observer today. Under current conditions, the 20% cut to family support services cannot hope to be remedied by the voluntary sector.

So the private sector is filling the gap. It is better equipped financially to cope with the new market of payment by results, social impact bonds and bidding for large contracts such as welfare to work. In allowing the private sector to expand at such a pace, Mr Cameron risks putting the encouragement of social engagement and the civic health of communities at peril.

The Localism Bill, in the hands of Eric Pickles, minister for community and local government, also appears a rum form of decentralisation. It gives Mr Pickles highly significant new powers and makes him lord of his own fiefdom. Local authorities no longer, for example, have a duty to involve residents in key decisions. Faith in the people this isn't.

The aim of the big society is social solidarity built from the bricks of centre-right ideas. As Steve Hilton, Mr Cameron's adviser, has said: "Nobody knows how it can be done." Innovation nevertheless is welcome as is reform to utilise the assets and capabilities of communities, improve society and tackle inequality. However, for that to happen, Mr Cameron must give greater direction; to prevent "slash-and-burn" cuts, to ensure equity and exercise greater command and control of his ministers, including diluting Mr Pickle's power.

Around £470m will help community groups to build the big society. Yet charities expect to lose £4.5bn as a result of spending cuts. Cuts aren't all bad. But the chasm between these two figures signals that on Wednesday, when addressing both the electorate and Tory members, Mr Cameron should elaborate further on precisely what he means by "compassionate".